U.S. patent application number 11/349865 was filed with the patent office on 2007-02-01 for method for advanced time-multiplexed etching.
Invention is credited to Tom Baehr-Jones, Michael J. Hochberg, Axel Scherer.
Application Number | 20070026682 11/349865 |
Document ID | / |
Family ID | 37694947 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070026682 |
Kind Code |
A1 |
Hochberg; Michael J. ; et
al. |
February 1, 2007 |
Method for advanced time-multiplexed etching
Abstract
A method of anisotropic plasma etching of a substrate material
through a window defined in an etching mask comprises the steps of:
disposing a hard mask material by injection of a precursor gas or
precursor liquid and plasma-activated deposition to form a hard
mask layer to form a temporary etch stop on the etching mask;
anisotropically plasma etching the hard mask layer by contact with
a reactive etching gas to leave a portion of the hard mask layer on
vertical walls of the window in the etching mask while exposing at
least part of the surface of the substrate; and selectively etching
material from the substrate underlying the exposed part of the
surface while leaving the portion of the hard mask layer on
vertical walls of the window in place.
Inventors: |
Hochberg; Michael J.;
(Pasadena, CA) ; Baehr-Jones; Tom; (Pasadena,
CA) ; Scherer; Axel; (Laguna Beach, CA) |
Correspondence
Address: |
Daniel L. Dawes;Myers Dawes Andras & Sherman LLP
Suite 1150
19900 MacArthur Boulevard
Irvine
CA
92612
US
|
Family ID: |
37694947 |
Appl. No.: |
11/349865 |
Filed: |
February 8, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60651821 |
Feb 10, 2005 |
|
|
|
Current U.S.
Class: |
438/710 ; 216/41;
216/67; 257/E21.038; 257/E21.235; 257/E21.257; 438/706;
438/733 |
Current CPC
Class: |
C03C 2218/34 20130101;
H01L 21/0337 20130101; H01L 21/31144 20130101; C03C 15/00 20130101;
C23F 4/00 20130101; H01L 21/3086 20130101 |
Class at
Publication: |
438/710 ;
438/706; 438/733; 216/067; 216/041 |
International
Class: |
C23F 1/00 20060101
C23F001/00; H01L 21/302 20060101 H01L021/302; C03C 15/00 20060101
C03C015/00 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] The present application was funded by the Naval Air Warfare
Center Aircraft Division under grant no. N00421-02-D-3223 Boeing
Subcontract No. KM5270. The U.S. Government has certain rights.
Claims
1. A method of anisotropic plasma etching of a substrate material
comprising etching a first mask disposed on a surface of the
substrate to define window through the first mask to a portion of
the surface of the substrate; disposing a hard mask material to
form a temporary etch stop on the first mask; anisotropically
plasma etching the hard mask layer by contact with a reactive
etching plasma or gas to leave a portion of the hard mask layer on
vertical walls of the window in the first mask while exposing at
least part of the surface of the substrate in the window;
selectively etching material from the substrate underlying the
exposed part of the surface in the window while leaving the portion
of the hard mask layer on vertical walls of the window in place;
and repeating disposing a hard mask material, anisotropically
plasma etching the hard mask layer and selectively etching material
from the substrate underlying the exposed part of the surface while
leaving the portion of the hard mask layer on vertical walls of the
window in place.
2. The method of claim 1 further comprising etching the substrate
when the window is defined and substrate exposed.
3. The method of claim 1 where anisotropic plasma etching is
performed by means of an inductively coupled plasma (ICP)
reaction.
4. The method of claim 1 where disposing a hard mask material
comprises disposing a hard mask material by injection of a
precursor gas or precursor liquid and plasma-activated deposition
to form a hard mask layer by means of a plasma enhanced chemical
vapor deposition (PECVD) reaction.
5. The method of claim 1 where disposing a hard mask material
comprises disposing a hard mask material by injection of a
precursor gas or precursor liquid and plasma-activated deposition
to form a hard mask layer by means of an ICP-PECVD reaction.
6. The method of claim 1 where disposing a hard mask material
comprises disposing a metal.
7. The method of claim 1 where disposing a hard mask material
comprises disposing silicon dioxide, silicon nitride, or silicon
oxynitrides.
8. The method of claim 1 where disposing a hard mask material
comprises disposing polysilicon.
9. The method of claim 1 where disposing a hard mask material
comprises depositing a hard mask material from a liquid source.
10. The method of claim 8 where disposing a liquid precursor of the
hard mask material comprises disposing TEOS or BPSG.
11. The method of claim 1 where disposing a hard mask material
comprises disposing silicon carbide.
12. The method of claim 1 where disposing a hard mask material
comprises disposing carbon, graphite, or diamond-like carbon.
13. The method of claim 1 where selectively etching material from
the substrate comprises selectively etching silicon.
14. The method of claim 1 where selectively etching material from
the substrate comprises selectively etching a Group III
semiconductor, or a Group V semiconductor.
15. The method of claim 14 where selectively etching a Group III-V
semiconductor comprises selectively etching gallium arsenide,
indium phosphide, gallium nitride, or gallium phosphode.
16. A method of anisotropic plasma etching of a substrate material
through a window defined in an etching mask comprising: disposing a
hard mask material by injection of a precursor gas or precursor
liquid and plasma-activated deposition to form a hard mask layer to
form a temporary etch stop on the etching mask; anisotropically
plasma etching the hard mask layer by contact with a reactive
etching gas to leave a portion of the hard mask layer on vertical
walls of the window in the etching mask while exposing at least
part of the surface of the substrate; and selectively etching
material from the substrate underlying the exposed part of the
surface while leaving the portion of the hard mask layer on
vertical walls of the window in place.
17. The method of claim 16 further comprising etching the substrate
when the window is defined and the substrate exposed.
18. The method of claim 16 further comprising repeating disposing a
hard mask material, anisotropically plasma etching the hard mask
layer and selectively etching material from the substrate
underlying the exposed part of the surface while leaving the
portion of the hard mask layer on vertical walls of the window in
place.
19. The method of claim 16 where anisotropically plasma etching is
performed by means of an inductively coupled plasma (ICP)
reaction.
20. The method of claim 16 where disposing a hard mask material
comprises disposing a hard mask material by means of a plasma
enhanced chemical vapor deposition (PECVD) reaction.
21. The method of claim 16 where disposing a hard mask material
comprises disposing a hard mask material by means of an ICP-PECVD
reaction.
22. The method of claim 16 where disposing a hard mask material
comprises disposing a metal, silicon dioxide, silicon nitride,
silicon oxynitrides, polysilicon, a liquid precursor of the hard
mask material, silicon carbide, carbon, graphite, or diamond-like
carbon, and where selectively etching material from the substrate
comprises selectively etching silicon, a Group III semiconductor,
or a Group V semiconductor.
Description
RELATED APPLICATIONS
[0001] The present application is related to U.S. Provisional
Patent Application, Ser. No. 60/651,821, filed on Feb. 10, 2005,
which is incorporated herein by reference and to which priority is
claimed pursuant to 35 USC 119.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention relates to the field of anisotropically
etching structures defined with an etching mask.
[0005] 2. Description of the Prior Art
[0006] Over the last 15 years, a number of companies have offered
silicon deep reactive ion etching systems utilizing the "Bosch" or
ASE process for etching structures in silicon, such as shown in
U.S. Pat. No. 5,501,893 incorporated herein by reference. This
process consists of a time-multiplexed etching scheme, consisting
of an isotropic polymer deposition, an anisotropic polymer removal,
and then a silicon etch step, which is generally isotropic. These
steps (the second and third steps are sometimes combined, because
the silicon etching step with SF.sub.6 also etches polymer) are
then repeated. The times of the various steps are tuned so as to
nearly eliminate etching of the mask layer and of the sidewalls,
but to allow etching of the trench.
[0007] There is a tradeoff in traditional, non-time multiplexed
etching, between the speed of an etch and how anisotropic it is,
and an ASE process allows the etch of very high aspect ratio
microstructures very quickly. Aspect ratios in excess of 30:1 are
often achieved and selectivities in excess of 70:1 to resist are
often achievable. This is because a fast, isotropic etch step can
be used to remove material quickly, while the polymer depositions
protect the sidewalls and force the etch to be anisotropic over
many steps.
[0008] A time-multiplexed etch is allows one to combine the
advantages of an isotropic etch with anisotropic profiles. The
isotropic etches are generally very fast and very selective,
because they can operate using species that react chemically with
the substrate. Although the switching of the etch conditions will
generally result in a small-scale scalloping on the sidewalls of
the etched areas, these can be reduced in scale to below 10
nanometers in modern processes by fast gas switching. Thus, etches
can be developed that have (1) extreme selectivity to mask
material, (2) high speed and (3) high anisotropy. The process is
thus performed with repetitive pulses of plasma gas etches and
plasma depositions and is referred to as a time-multiplexed
etch.
[0009] The Bosch process, which uses a polymer deposition
alternated with an SF.sub.6 based etch of silicon in a plasma
reactor is well-known. However, it is limited to silicon, because
the chemistry relies upon the deposition of a polymer that only
stands up to fluorine based chemistry. Fluorine chemistry, while
efficient for etching silicon, is not the most efficient chemistry
for etching most materials.
BRIEF SUMMARY OF THE INVENTION
[0010] The illustrated embodiment of the invention is distinct from
the prior art, like the Bosch process, because it incorporates the
deposition of a hard mask material, which makes a time-multiplexed
etch usable for generalized substrate materials, rather than only
for silicon as is the case for the Bosch process. Generally, a hard
mask material is a material which has an inorganic chemical
composition, as contrasted with polymers or organic photoresists,
which are not hard mask materials.
[0011] For example, in the illustrated embodiment the invention is
a method of anisotropic plasma etching of a substrate material
through a window defined in an etching mask comprising the steps
of: (1) depositing a hard mask material by injection of a precursor
gas or precursor liquid and plasma-activated deposition to form a
hard mask layer to form a temporary etch stop on the etching mask;
(2) anisotropically plasma etching the hard mask layer by contact
with a reactive etching gas to leave a portion of the hard mask
layer on vertical walls of the window in the etching mask while
exposing at least part of the surface of the substrate; and (3)
selectively etching material from the substrate underlying the
exposed part of the surface while leaving the portion of the hard
mask layer on vertical walls of the window in place. These steps
can be implemented starting with any of the three steps, since this
is a cyclical process. The anisotropy of the etch may be determined
not only by the directionally dependent chemical affinities of the
etch and the material to be etched, but also by the dynamic nature
of a plasma etch process in which the impinging ions have a
direction, velocity and acceleration. In some instance the
anisotropy may be substantially determined only by geometry of the
window and dynamic parameters of the plasma etch.
[0012] The method may also comprise the foregoing steps with the
understanding that the claimed process may begin at the
initialization of any of the above disclosed steps following the
definition of the window through the etching mask.
[0013] The method further comprises repeating depositing a hard
mask material, anisotropically plasma etching the hard mask layer
and selectively etching material from the substrate underlying the
exposed part of the surface while leaving the portion of the hard
mask layer on vertical walls of the window in place.
[0014] In the illustrated embodiments the step of anisotropically
plasma etching is performed by means of an inductively coupled
plasma (ICP) reactive ion etch, or by a conventional reactive ion
etch in a parallel-plate reactor.
[0015] In the illustrated embodiments the step of disposing a hard
mask material comprises disposing a metal, silicon dioxide, silicon
nitride, silicon oxynitrides, polysilicon, a liquid precursor of
the hard mask material, silicon carbide, carbon, graphite, or
diamond-like carbon, through plasma-enhanced chemical vapor
deposition (PECVD). The step of selectively etching material from
the substrate comprises selectively etching silicon, a Group III
semiconductor, or a Group V semiconductor using a plasma-based
etch.
[0016] While the apparatus and method has or will be described for
the sake of grammatical fluidity with functional explanations, it
is to be expressly understood that the claims, unless expressly
formulated under 35 USC 112, are not to be construed as necessarily
limited in any way by the construction of "means" or "steps"
limitations, but are to be accorded the full scope of the meaning
and equivalents of the definition provided by the claims under the
judicial doctrine of equivalents, and in the case where the claims
are expressly formulated under 35 USC 112 are to be accorded full
statutory equivalents under 35 USC 112. The invention can be better
visualized by turning now to the following drawings wherein like
elements are referenced by like numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1a-1f is a sequence of side cross sectional
diagrammatic depictions of the formation of a trench in a substrate
using the hard masking layer and etching techniques of the
invention.
[0018] The invention and its various embodiments can now be better
understood by turning to the following detailed description of the
preferred embodiments which are presented as illustrated examples
of the invention defined in the claims. It is expressly understood
that the invention as defined by the claims may be broader than the
illustrated embodiments described below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Recently a number of companies, most notably Oxford
Instruments, Sentech and STS, have begun to offer inductively
coupled plasma, plasma enhanced chemical vapor deposition systems
(ICP PECVD). These are apparatus or tools that utilize an
inductively coupled remote plasma chamber in order to do plasma
enhanced chemical vapor deposition of oxide and nitride layers, as
well as diamond like carbon (DLC), oxynitrides, polycrystalline
silicon, germanium and silicon-germanium complexes. The potential
also exists for the deposition of metals and all of the other
materials for which conventional plasma enhanced chemical vapor
deposition systems (PECVD) are currently used.
[0020] Plasma enhanced CVD (PECVD) uses a plasma or glow discharge
with a low pressure gas, to create free electrons which transfer
energy into the reactant gases. This allows the substrate to remain
at a lower temperature than in other chemical vapor deposition
(CVD) processes. A lower substrate temperature is the major
advantage of PECVD and provides film deposition methods for
substrates that do not have the thermal stability necessary for
other processes that require higher temperature conditions. In
addition, PECVD can enhance the deposition rate when compared to
thermal reactions alone, and produce films of unique compositions
and properties.
[0021] Also, the systems that are used for conventional PECVD are
not compatible with high rate etch processes, in general, because
of the relatively low rates of substrate etching that can be
achieved in conventional PECVD tools. However, there is no
intrinsic limitation of the processes described here to ICP or any
other decoupled reactor geometry such as ECR (electron cyclotron
resonance). The use of such a reactor is preferred for the
processes disclosed herein.
[0022] With the new combined ICP PECVD/ICP RIE systems, it becomes
possible to construct a system that does both ICP PECVD deposition
and ICP etching, since both are plasma processes that can be
performed in the same apparatus. The speeds of the current
generation of RF matching networks, pumps and mass flow controllers
allows for the extremely rapid switching of gas chemistries in a
single chamber, with extremely short residence times. This is thus
referred to as a pulsed plasma process. This introduces the
possibility of creating a time-multiplexed, fast process for
etching of non-silicon materials, using hard masks and non-fluorine
chemistries.
[0023] In the illustrated embodiment we use a time multiplexing
scheme to enhance the selectivity of an etch, where the mask layer
is formed by ICP PECVD based growth of a hard mask layer 16. The
etch step of the substrate 10 is an ICP based etch step, performed
in the same chamber. A third anisotropic etch step for removal of
the hard mask 16 over the features to be etched can be included as
well.
[0024] Hard mask materials 16 may include, but are not limited to,
metals, silicon nitride, silicon dioxide, silicon oxynitride, poly
silicon, and poly germanium. Materials to be etched may include
oxides, nitrides, semiconductors, metals, and any other etchable
materials.
[0025] The condition for this process to work is the existence of a
hard mask layer 16 giving a high selectivity for etching of the
substrate material 10. The hard mask layer 16 is defined by two
conditions. Any mask layer that can be isotropically disposed or
deposited on the surface of the substrate 10 is contemplated as
being within the scope of the invention. Similarly, the hard mask
layer 16 must be associated with a corresponding anisotropic etch
chemistry for the mask material.
[0026] An example of such a system is silicon as a substrate 10 and
silicon dioxide as a mask material 16, using fluorinated gasses
(C.sub.4F.sub.8) to etch the mask 16 and either Cl or SF.sub.6 to
etch the substrate 10. Another example is a polymer substrate 10
with silicon dioxide or nitride as a mask material. A third example
is silicon dioxide as a material for substrate 10 with metal, e.g.
chrome, or aluminum, PECVD'ed as the etch mask 16.
[0027] Any material system where a mask material 16 can be
deposited in a highly isotropic manner, where there exists a highly
anisotropic etch achievable in an ICP reactor for that material 16,
and where there is an etch with a high selectivity between said
mask material 16 and the substrate material 10, either an isotropic
or anisotropic etch, is a candidate for the etching strategy of the
invention. There is an extensive literature on various etching
chemistries and selectivity information to various mask material,
all of which is contemplated as being within the scope of the
spirit and teachings of the invention. The claims are thus not to
be understood a necessarily limited to the given illustrated
embodiments.
[0028] Thus, the illustrated embodiments explicitly include a
method of anisotropic plasma etching of an arbitrary substrate
material to provide laterally defined recess structures therein
through an etching mask employing a plasma as illustrated
diagrammatically in FIGS. 1a-1d. The method comprises the steps of
anisotropic plasma etching the surface of the substrate material 10
by contact with a reactive etching plasma to remove material 14
from the surface 12 of the substrate material 10 and to provide
exposed surfaces 12 as shown in the side cross-sectional view of
FIG. 1a. Next as shown in FIG. 1b a hard mask material 16 is
disposed or deposited onto surface 12 and material 14 through
injection of a precursor gas or liquid and plasma-activated
deposition to form a hard mask layer 16 which provides a temporary
etch stop. Anisotropic etching of layer 16 occurs as shown in FIG.
1c leaving at least a portion of layer 16 on the vertical walls 18
defined in openings in material 14. Anisotropic plasma etching of
material 10 through exposed surface 12 is performed as depicted in
FIG. 1d.
[0029] The steps of depositing a hard mask material 16 and then
subsequent depositions 16' and anisotropic plasma etching are then
repeated in any order any many times as desired, repeating the
sequence of steps from FIG. 1b to FIG. 1d, thereby deepening trench
20 as indicated in FIG. 1f. The thickness of layers 16 and 16' in
FIG. 1f on walls 18 has been exaggerated in the figures for ease of
visualization, but in the actual instance the thickness of layers
16 and 16' are such that stepped nature of walls 18 or trench 20 is
minimal. According to the preferred embodiments the process may
begin after the completion of the step shown in FIG. 1a where the
window 12 is defined, after the completion of the step shown in
FIG. 1d where the trench 20 is created, or after the completion of
the step shown in FIG. 1f where the trench 20 has been deepened.
Similarly, substrate 10 may be subjected to an additional
conventional etching step where a window 12 is defined and
substrate 10 exposed, such as after the completion of any of the
steps illustrated in FIGS. 1a, 1c, 1d or 1f.
[0030] In the illustrated embodiment the plasma is generated in an
inductively coupled reactor. The deposition step is performed with
a conventional PECVD reaction. In particular the deposition step is
performed with an ICP PECVD reactor.
[0031] In one embodiment the deposited material 16 is a metal,
silicon dioxide, silicon nitride, silicon oxynitrides, polysilicon,
a liquid precursor, such as tetra ethyl ortho silicate (TEOS) or
borophosphosilicate glass (BPSG), silicon carbide, carbon,
graphite, or diamond like carbon. The substrate material 10 is
silicon, a Group III or V semiconductor, such as gallium arsenide,
indium phosphide, gallium nitride, or gallium phosphode.
[0032] An illustrative listing of substrates, substrate etchants
and hard mask materials is given below in Table 1, which is not
exhaustive nor limiting of the scope of the invention. For each of
the combinations listed in Table 1, the hard mask materials work
well as masks for plasma etching as disclosed above. Further, the
chemistries in the combinations provide high rate and high
selectivity isotropic etching. TABLE-US-00001 TABLE 1 Substrate
Substrate Etch Hard Mask GaAs Cl/Ar, BCl.sub.3/Ar, SiCl.sub.4/Ar
SiO.sub.2, SiN, Cr, Ni AlAs Cl/Ar, BCl.sub.3/Ar, SiCl.sub.4/Ar
SiO.sub.2, SiN, Cr, Ni InGaAsP Cl/Ar, H.sub.2/CH.sub.4,
Hl/Cl.sub.2/Ar, SiO.sub.2, SiN, Cr, Ni HBr/Ar ZnSe Cl/Ar,
BCl.sub.3/Ar SiO.sub.2, SiN, Cr, Ni GaN Cl/Ar, Cl/Xe, BCl.sub.3/Ar
SiO.sub.2, SiN, Cr, Ni InGaN Cl/Ar, Cl/Xe, BCl.sub.3/Ar SiO.sub.2,
SiN, Cr, Ni C (diamond and DLC) O.sub.2, NO.sub.2 metals,
SiO.sub.2, SiN SiC CHF.sub.3, C.sub.2F.sub.6, C4F.sub.8 Al, Ni, Cr
SiN CHF.sub.3, C.sub.2F.sub.6, C4F.sub.8 Al, Ni, Cr SiO.sub.2
CHF.sub.3, C.sub.2F.sub.6, C4F.sub.8 Al, Ni, Cr GaSb Cl/Ar,
BCl.sub.3/Ar, SiCl.sub.4/Ar SiO.sub.2, SiN, Cr, Ni LiNbO.sub.5
Cl/CHF.sub.3/Ar Cr, Ni W CF.sub.4, CHF.sub.3, C.sub.2F.sub.6,
C.sub.4F.sub.8 Cr, Ni Al Mo ClF.sub.3 Ni, Cr Al BCl.sub.3, Cl/Ar
SiO.sub.2, SiN, Cr, Ni
[0033] Many alterations and modifications may be made by those
having ordinary skill in the art without departing from the spirit
and scope of the invention. Therefore, it must be understood that
the illustrated embodiment has been set forth only for the purposes
of example and that it should not be taken as limiting the
invention as defined by the following invention and its various
embodiments.
[0034] For example, instead of PCP PECVD being used for the
deposition step, it is also possible to practice the invention
using atomic layer deposition (ALD). Atomic layer deposition (ALD),
originally known as atomic layer epitaxy (ALE), is an advanced form
of vapor deposition. ALD processes are based on sequential
self-saturated surface reactions. Examples of these processes are
described in detail in U.S. Pat. Nos. 4,058,430 and 5,711,811
incorporated herein by reference. The deposition processes benefit
from the usage of inert carrier and purging gases, which make the
system fast. Due to the self-saturating nature of the process, ALD
enables almost perfectly conformal deposition of films on an
atomically thin level. The technology was initially developed for
manufacturing thin film structures for electroluminescent flat
panel displays and for conformal coating of chemical catalysts that
desirably exhibited extremely high surface area. More recently, ALD
has found application in the fabrication of integrated circuits.
The extraordinary conformality and control made possible by the
technology lends itself well to the increasingly scaled-down
dimensions demanded of state-of-the-art semiconductor processing. A
method for depositing thin films on sensitive surfaces by ALD is
described in WO 01/29839. In addition, ALD can easily be performed
in-situ within the same plasma reactor as an ICP deposition
process.
[0035] Therefore, it must be understood that the illustrated
embodiment has been set forth only for the purposes of example and
that it should not be taken as limiting the invention as defined by
the following claims. For example, notwithstanding the fact that
the elements of a claim are set forth below in a certain
combination, it must be expressly understood that the invention
includes other combinations of fewer, more or different elements,
which are disclosed in above even when not initially claimed in
such combinations. A teaching that two elements are combined in a
claimed combination is further to be understood as also allowing
for a claimed combination in which the two elements are not
combined with each other, but may be used alone or combined in
other combinations. The excision of any disclosed element of the
invention is explicitly contemplated as within the scope of the
invention.
[0036] The words used in this specification to describe the
invention and its various embodiments are to be understood not only
in the sense of their commonly defined meanings, but to include by
special definition in this specification structure, material or
acts beyond the scope of the commonly defined meanings. Thus if an
element can be understood in the context of this specification as
including more than one meaning, then its use in a claim must be
understood as being generic to all possible meanings supported by
the specification and by the word itself.
[0037] The definitions of the words or elements of the following
claims are, therefore, defined in this specification to include not
only the combination of elements which are literally set forth, but
all equivalent structure, material or acts for performing
substantially the same function in substantially the same way to
obtain substantially the same result. In this sense it is therefore
contemplated that an equivalent substitution of two or more
elements may be made for any one of the elements in the claims
below or that a single element may be substituted for two or more
elements in a claim. Although elements may be described above as
acting in certain combinations and even initially claimed as such,
it is to be expressly understood that one or more elements from a
claimed combination can in some cases be excised from the
combination and that the claimed combination may be directed to a
subcombination or variation of a subcombination.
[0038] Insubstantial changes from the claimed subject matter as
viewed by a person with ordinary skill in the art, now known or
later devised, are expressly contemplated as being equivalently
within the scope of the claims. Therefore, obvious substitutions
now or later known to one with ordinary skill in the art are
defined to be within the scope of the defined elements.
[0039] The claims are thus to be understood to include what is
specifically illustrated and described above, what is
conceptionally equivalent, what can be obviously substituted and
also what essentially incorporates the essential idea of the
invention.
* * * * *